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Billie Eilish

Singer Billie Eilish thought her chart-topping single Bad Guy would be a flop.

The star's song with her musician brother Finneas has finally hit the top spot on America's Billboard Hot 100 chart after being released in March, and the 17-year-old admits she feels the accomplishment is too good to be true.

"What's funny about it is I actually thought it would flop... because the chorus doesn't have a hook - at least what we wrote as the chorus," Billie tells Billboard. "My brother and I actually sat in his room trying to write something else over that but we couldn't do it because nothing else worked.

"For some reason people do like it and it's huge now. It's one of my favourite songs I've ever made. It's my favourite to perform, it's so fun. I'm so proud of that song."

Billie and Finneas' Bad Guy was second to rapper Lil Nas X's record-making song Old Town Road for several weeks before climbing to the number one position.

"It's crazy to think about Bad Guy as a well-known song," Billie laughs. "Nobody doesn't know (Old Town Road), you know? Having my song be above that song right now (on the Hot 100 list) is shocking to me.

"I think Lil Nas is so sweet; I met him a couple weeks ago. It's so not a competition, it's just funny... I don't really care (about numbers). It's just a fun thing that happens in careers. It doesn't really matter, but it's kind of interesting, you know?"